Abstract: A foreign matter detection device, for detecting a foreign matter on a photomask of transparent material with opaque patterns formed thereon, includes a laser source for emitting an S-polarized laser beam so as to impinge on a first surface of the photomask which reflects a P-polarized laser beam. A light source is provided to illuminate the photomask at an opposed surface to the first surface, from which a light transmits. This reflected P-polarized laser beam and transmitted light enters, through a condenser lens and a deflection plate, into a CCD in which an image representing the condition of the impinged surface is obtained. Since the P-polarized laser beam indicative of the corner edge of the pattern is offset by the transmitted light passing around the same corner edge, the pattern image is obscured and foreign matter is distinguishable in the obtained image.